Impact line printers are commonly used as readout devices for automated medical instrumentation, weighing devices, and digital computers. In the impact line printer, the type is carried on a continuously moving belt or drum and the paper and ribbon are locally impacted against the type face by a high velocity, small mass pivoted print hammer. The print hammer is driven by an actuator, typically an electrical solenoid, and makes contact with the paper for an extremely short time interval after which time it bounces back to its rest position. Since printing is "on the fly", i.e. the print drum or belt is constantly moving, a controller times the application of the current pulse to the actuator a sufficient time in advance such that the print hammer impacts the paper in time coincidence with the selected print character position.
In the current state of the art, impact line printer devices have been constructed with high print densities. However, the close spacing between the print hammers has been accomplished by an increase in cost and complexity. One type of prior art device uses sophisticated and expensive solenoid actuators having a very thin cross-sectional configuration so that the magnets may be stacked closely adjacent one another. Another type of prior art impact line printer device stacks the solenoids vertically, i.e. the solenoids are mounted one on top of each other. This arrangement substantially increases the manufacturing costs of the solenoid support structure, requires the use of long push rods from those solenoids stacked one or more solenoid layers away from the print hammers and creates an overall structure having a greater vertical dimension that may be tolerated in certain applications.